Saturday, August 26, 2006

RTFR ....

The first of the US Climate Change Science Synthesis and Assessment Products was released in April 2006, and what commentary there was on the report concentrated on the reconciliation of temperature trends from surface measurements, satellites, balloons and more. Fair enough, that was what the title of the report was "Temperature Trends in the Lower Atmosphere - Understanding and Reconciling Differences"

However, if you go further, specifically to Chapter 5: How well can the observed vertical temperature changes be reconciled with our understanding of the causes of these temperature changes? You find a detailed discussion of agreement between models and observations. It being late, I will simply quote the relevant conclusions of this OFFICIAL US Government document:

1. Both human and natural factors have affected Earth’s climate. Computer models are the only tools we have for estimating the likely climate response patterns (“fingerprints”) associated with different forcing mechanisms.
To date, most formal fingerprint studies have focused on a relatively small number of climate forcings. Our best scientific understanding is that:
• Increases in well-mixed greenhouse gases (which are primarily due to fossil fuel burning) result in largescale warming of the Earth’s surface and troposphere, and cooling of the stratosphere.
• Human-induced changes in the atmospheric burdens of sulfate aerosol particles cause regional cooling of the surface and troposphere.
• Depletion of stratospheric ozone cools the lower stratosphere and upper troposphere.
• Large volcanic eruptions cool the surface and troposphere (for 3 to 5 years) and warm the stratosphere (for 1 to 2 years).
• Increases in solar irradiance warm globally throughout the atmospheric column (from the surface to the stratosphere).
2. Results from many different fingerprint studies provide consistent evidence of a human influence on the three-dimensional structure of atmospheric temperature over the second half of the 20th century.

Robust results are:
• Detection of greenhouse-gas and sulfate aerosol signals in observed surface temperature records.
• Detection of an ozone depletion signal in stratospheric temperatures.
• Detection of the combined effects of greenhouse gases, sulfate aerosols, and ozone in the vertical structure of atmospheric temperature changes (from the surface to the stratosphere).
3. Natural factors have influenced surface and atmospheric temperatures, but cannot fully explain their changes over the past 50 years.
There is more which we will get into later. The principal difference remaining between models and observation is
• For globally averaged temperatures, model-predicted trends in tropospheric lapse rates are consistent with observed results.
• In the tropics, most observational data sets show more warming at the surface than in the troposphere, while most model runs have larger warming aloft than at the surface.

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